1. Field of the Invention
An optical range simulator device.
2. Description of the Prior Art
Advanced electro-optical weapons delivery systems require sophisticated test methods to assure measurement integrity. Techniques are required to confirm accurate ranging of optical radars, proper boresighting of all optical channels, and round trip system performance. A straightforward and convenient means of testing such a system is desirable.
In the past the performance of such systems have been tested primarily by two methods: (1) through the use of a surveyed outdoor optical radar range having targets of known characteristics; and, (2) through the use of an active optical transponder directly coupled to the system undergoing test. Method (1) requires considerable terrain area, a fixed plant, and presents weather and safety problems. Method (2) requires a critical optical interface, particularly with respect to boresighting, and it is difficult for the transponder to simulate the signature of returns from real targets. The magnitude of the transponded returns must be known if the receiver sensitivity contribution to oversall system performance is to be established. Such magnitudes are not readily calibrated at the wavelengths of interest, particularly for short pulses and signal levels close to optical receiver thresholds. Timing of the transponded returns is critical to range accuracy, and it is not straightforward to achieve and maintain the required accuracy using inexpensive radiation sources, for example.
In the more recent past, applicants have devised several versions of a passive optical range simulator employing a coiled length of optical fiber to act as an optical delay medium for acceptance and return of pulsed optical energy to and from the optical radar ranger system undergoing test. Both versions have been used successfully in ranger system production line tests; a first version from mid 1975 until late 1976 and a second version from late 1976 until at least the filing date of the present patent application intended to cover such second version.
The earlier-used version employed a collimator assembly with reflective optics as an optical interface with the ranger system under test, and a relay lens to furnish additional focused demagnification at the fiber coil entrance. An anti-reflection property of the collimator entrance window was relied on for minimizing unwanted reflection of energy back into the input of the system under test. An attenuator stack of flat parallel slightly-tilted glass elements was used in advance of the relay lens for fine adjustment of attenuation. There was no mechanism that established the relationship between the boresight axis of the system under test and that of the collimator/range simulator combination, nor was there one to ensure that the beam system of the system under test fell completely within the clear aperture of the collimator assembly.